I have had a couple reasons presented to me on this. One is the previous engine wasn't winterized and cracked and the replacements are not blue. The other, well gets a bit convoluted.

LT-1 in the 30th Anniversary is 350 HP, whereas the standard LT-1 was 330 or 335 HP. If it is blue, 350 HP, if it is not, possibly 330 HP....which isn't to say the black engine didn't have the different cam installed in it to make it 350 HP and wasn't painted blue? I can go back to my source to see if that may be the case here. I have only seen a couple 30th boats without the blue block.

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2003 ProStar 197, MCX and Powerslot.
RON PAUL FOR PRESIDENT
"When the government lies, the truth becomes a traitor."